Licorice and a water extract thereof have been used as galenicals having analgesic and antispasmodic actions and an expectorant action, or in food applications. Since glycyrrhizin (glycyrrhizinic acid), which is a main component of licorice, is about 200 times sweeter than sucrose, it is also used as a sweetening agent.
It has also been confirmed that hydrophobic components extracted from licorice or a water-extracted residue of licorice with an organic solvent, such as ethanol, acetone, or ethyl acetate, have many useful effects, such as an antioxidant effect, an antibacterial effect, an enzyme inhibitory effect, an antitumor effect, an antiallergic effect, and an antiviral effect. Furthermore, recent research has found that the hydrophobic components of licorice have a hypoglycemic action and a lipid metabolism-improving action (WO02/47699).
In order to extract such hydrophobic components from licorice, organic solvents are exclusively used. For example, each of Japanese Unexamined Patent Application Publications Nos. 1-149706 and 3-109314 discloses an example of extraction with a hydrophobic organic solvent; Japanese Unexamined Patent Application Publication No. 2-204495 discloses an example of extraction with a mixed solvent of a hydrophobic organic solvent and a small amount of water-soluble organic solvent; Japanese Unexamined Patent Application Publication No. 7-53393 discloses an example of extraction with water and/or a water-soluble organic solvent (preferably, hot water); and Japanese Unexamined Patent Application Publication No. 1-157909 discloses an example of extraction with one of a wide variety of water-soluble organic solvents and hydrophobic organic solvents.
However, the resulting hydrophobic components of licorice do not substantially dissolve in water and common oil, and the extract obtained with such an organic solvent easily cakes and colors, thus being unstable. Therefore, the extract must be formulated so as to be easy to handle and stable. In any of the methods described above, the organic solvent used for extraction results in many unsolved problems, for example, a high production cost and a significant adverse effect on the environment.